1. Field of the Invention
The present invention relates to testing, measuring, analyzing or predicting bioaccumulation and is particularly related to a method for laboratory testing or determining log Pow values of chemical substances for relating to the bioaccumulation of such substances. The method is notably suitable for measuring or evaluating bioaccumulation of surfactants, although the method may also be used for measuring or evaluating bioaccumulation of other chemical substances.
2. Description of Relevant Art
Bioaccumulation is generally defined as the process through which a chemical increases in concentration in a biological organism over time when compared to the concentration of the chemical in the environment. Compounds accumulate in living things any time they are taken up and stored faster than they are broken down, metabolized or excreted. The process is normal and can be helpful to life, as in the storage of vitamins, for example. However, the process can result in injury to life when the equilibrium between exposure and bioaccumulation is overwhelmed. The extent of bioaccumulation depends on the concentration of the chemical in the environment, the amount of chemical coming into an organism from the food, air or water, and the time it takes for the organism to acquire the chemical and then store, metabolize or degrade, and excrete it. The nature of the chemical itself, such as its solubility in water and fat, affects its uptake and storage; the ability of the organism to degrade and excrete the chemical also affects its uptake and storage. Understanding the dynamic process of bioaccumulation is generally viewed as important in protecting humans and other organisms from adverse effects from chemical exposure. Consequently, bioaccumulation has become a critical consideration in the regulation of chemicals.
Industries using chemicals in the environment are increasingly faced with regulations concerning bioaccumulation of those chemicals. The oil and gas industry has varying guidelines and regulations in many countries worldwide relating to chemicals used in the search for and production of hydrocarbons from subterranean formations in those countries. Some regulations require testing of individual components of chemicals used. For compliance with such guidelines and regulations, the industry tests its chemicals and chemical components, often by test methods or techniques also prescribed, recommended, and/or approved in the guidelines or regulations.
One such test is the OECD Guideline for Testing of Chemicals No. 117, concerning the Partition Coefficient (n-octanol/water), High Performance Liquid Chromatography (HPLC) Method, incorporated herein in its entirety by reference and available from the Organisation for Economic Co-operation and Development in Paris, France. This test is performed on analytical columns packed with a commercially available solid phase containing long hydrocarbon chains (e.g., C8-C18) chemically bound onto silica. Chemicals injected onto such a column move along it by partitioning between the mobile solvent phase and the hydrocarbon stationary phase. The chemicals are retained in proportion to their hydrocarbon-water partition coefficient, with water-soluble chemicals eluted first and oil-soluble chemicals eluted last. This pattern enables the relationship between the retention time on a reverse-phase column and the n-octanol/water partition coefficient to be established. The partition coefficient is deduced from the capacity factor, k, given by the formula:   k  =                    t        R            -              t        o                    t      o      where tR is the retention time of the test substance, and to is the dead-time, i.e., the average time an unretained molecule needs to pass through the column. Quantitative analytical methods are not needed and only the retention times are measured.
The partition coefficient (P) is the ratio of the equilibrium concentrations of a dissolved substance in a two-phase system consisting of two largely immiscible solvents. For n-octanol and water, the partition coefficient is the quotient of the concentrations of the two, expressed as follows, but usually written in the form of its logarithm to base ten:       P    ow    =            c              n        ⁢                  -                ⁢        octanol                    c      water      
Pow is a key parameter in studies of the environmental impact of chemical substances. The OECD Guideline No. 117 states that there is a highly-significant relationship between the Pow of substances and their bioaccumulation in fish and that Pow is useful in predicting adsorption on soil and sediments and in establishing quantitative structure-activity relationships for a wide range of biological effects.
The HPLC method or test can be used in determining Pow values in the range log Pow between 0 and 7. A preliminary estimation of Pow, generally done through known calculation methods, is needed. When the Pow values are in the range log Pow between −2 and 4, another test has been used. That test is the OECD Guideline for Testing of Chemicals No. 107, called the Partition Coefficient (n-octanol/water): Shake-Flask Method, which is incorporated herein in its entirety by reference and available from the Organisation for Economic Co- operation and Development in Paris, France.
The Shake-Flask Method is based on the principle that the Nernst partition law applies at constant temperature, pressure and pH for dilute solutions. OECD Guideline No. 107 states that the law strictly applies to a pure substance dispersed between two pure solvents and when the concentration of the solute in either phase is not more than 0.01 mole per liter. If several different solutes occur in one or both phases at the same time, the results may be affected. Dissociation or association of the dissolved molecules cause deviations from the partition law.
Neither the HPLC Method nor the Shake-Flask Method may be used for determining log Pow, values for measuring or evaluating bioaccumulation for chemicals that are considered surface active, or for surfactants. Nevertheless, surfactants are commonly used in drilling and well treating fluids. A need exists for effective new techniques or methods for determining the Pow values of various surfactants.